High energy ignition device

ABSTRACT

A spark igniter for gas turbine engines, having passage means for positioning a small quantity of liquid fuel directly in the path of the spark, which fuel is vaporized, ignited, and expelled as a jet of flame into the combustion chamber to ignite the main fuel flow.

[ Aug. 7, 1973 United States Patent 1 Zoll 2,574,495 11/1951Parker...................,.. .....60/39.82P 3,057,159 10/1962Benedict....................l....60/39.82S

1 N M r we vr. B Dm NC m 0 m1 H m mm R EA NE m p. mm 4 M MW [73]Assignee: Curtiss-Wright Corporation, FOREIGN PATENTS OR APPLICATIONSWood-Ridge, NJ.

Dec. 22, 1971 1,018,963 2/1966 Great Britain.....;.......,.... 60/3982 S765,175 1/1957 Great Britain.....,....,..,.... 60/39 82 S [22] Filed:

Appl' 210975 Primary Examiner-Clarence R. Gordon AssistantExaminer-Warren Olsen P6 2 7 c E2 0 1 S 2 3 9 3 0 6 [52] US. Cl.AttorneyRaymond P. Wallace et al. [51] Int.

h c r a e ABSTRACT [56] References Cited UNITED STATES PATENTS A sparkigniter for gas turbine engines, having passage L m a u t e m m mu." 1a" e aB bug-1 aOOm RCLS 983 4565 9999 1111 ///l 250 l 1 6 29 8480 2 4 22 9582 5687 1 2232 60/39 82 S 60/3982 S 60/3982 P 60/3982 S 4 Claims, 2Drawing Figures 7 4 ZT I L Z 2 & -X\ E j 1 /z T x 1 x /w /w /H .Lr 0 \ln 2 .x XXX K a m 1 H /////1 U I 1 HIGH ENERGY IGNITION DEVICE BACKGROUNDOF THE INVENTION This invention pertains to gas turbine engines, andmore particularly to a means of lighting off a gas turbine engine fromrest state. Successful and reliable ignition of a gas turbine,particularly in the cold state, requires a high energy ignition systemto assure that sufficient heat is released to ignite a self-propagatingflame front, since fuel vaporization in the cold engine is relativelylow. High energy electrical ignition systems as commonly used for thispurpose range from 4 to 20 joules of stored electrical energy, and moreparticularly toward the higher end of that range; Such a system isnecessarily complex and expensive.

SUMMARY OF THE INVENTION The present invention provides a high energyignition device requiring only 0.5 to 2 joules of stored electricalenergy, the remainder of the igniting energy being supplied bypositioning a very small quantity of liquid fuel between the electrodesdirectly in the path of the spark. The spark generated by the powersupply of relatively low energy vaporizes the fuel and ignites it,producing a sudden expansion of flaming gas which is propelled as a ballof flame from the igniter into the main fuel and air mixture. The powersupply of the ignition device is pulsed at about one to times persecond, preferably about three times. However, since it operates foronly a few seconds until a self-propagating flame front is establishedin the combustor, after which the priming fuel is shut off, the fuelconsumed by the igniter is negligible. It would amount to about half apound of fuel for a full hour of operation.

It is therefore an object of this invention to provide a reliableignition device with low electrical power requirement.

It is another object to provide an ignition device in which theelectrical energy is supplemented by primary fuel in the path of thespark.

The foregoing objects and advantages and other ancillary thereto will beunderstood on reading the following specification in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevationof the igniter of the invention, mounted in a combustion chamber; and

FIG. 2 is a cross-section taken on line 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a fragment of thewall 11 of a turbine combustion chamber, with an igniter 12 mountedthereon and projecting into the combustion zone. A head member 13 has amounting flange 14 which is secured to the exterior of the combustorwall 11 by screws as shown, or by other convenient means. The combustorwall is provided with an aperture 16, through which a tubular well 17borne by the head member 13 extends into the combustion zone.

A tubular insulator 18, formed of fused aluminum oxide or other suitablehigh temperature insulating material, is positioned in the well 17 andseated against the inner end wall thereof, the insulator also extendingthrough the head 13. The insulator may be retained by any convenientmeans. In the example shown, the outer end of the aperture through thehead is threaded, and an annular gland l9 surrounding the insulator isscrewed into the thread, seating against a shoulder 21 of the insulatorto hold it firmly in place. An electrode 22 is coaxially disposed in theinner diameter of the tubular insulator, maintained in position by agastight packing 23 surrounding the electrode within the insulator tube.

The outer diameter of insulator 18 is slightly less than the innerdiameter of well 17, so that an annular channel 24 exists between thetwo parts. Head 13 is provided with a connection 26 which may be eithera nipple or a tapped thread, as shown, for attaching a fuel line. Apassage 27 communicates between the connection 26 and the annularchannel 24, whereby the channel may receive a supply of fuel from a tank(not shown).

The inner end portion of the insulator 18 has its inner diameterexpanded in a funnel-shaped portion 28 for a short distanceapproximately equal to the length of the spark path, and the flat endface of the insulator, which is seated on the inner end wall 15 of well17, is provided with a plurality of shallow diametral slots thereacrosswhich communicate between the funnel portion 28 and the annular channel24, permitting flow of fuel to the funnel portion. If desired the wallof the insulator may have holes drilled through it a little above theend, instead of slots, so that the fuel is delivered to some portion ofthe funnel wall. The end wall 15 of well 17 has a coaxial aperture 31therein of approximately the same diameter as the larger end of funnelportion 28. The central electrode 22 extends only as far inward as thesmaller end of the funnel portion, and the spark gap is between theinner end 32 of the electrode and the edge of aperture 31.

In operation, when it is desired to light off the engine a valve (notshown) is opened between the fuel supply and the fuel connection 26 inthe igniter device. Very little pressure is needed to feed the fuel, oneor two pounds above atmospheric being sufficient. In many cases theposition of the fuel tank at a normal distance above the igniter willprovide sufflcient pressure. Fuel travels through passage 27 into theannular channel 24, and thence through passages 29 to the inner surfaceof funnel 28. To some extent the fuel will creep upward on the innerdiameter of the funnel if slots rather than holes are used; at most onlya few drops are required at the point of arc. The power supply,containing capacitor-stored electrical energy of 0.5 to 2 joules, isactivated, and the arc strikes along the inner wall of the funnel,vaporizing and igniting any fuel present. The flaming gases arepropelled by the force of their own expansion out of the funnel as aball of flame into the fuel-air mixture of the combustor. The ignitermay continue to operate for a few seconds, pulsing at a rate of aboutthree times per second, but only a very short period of operation isrequired to reliably ignite the combustor with a self-propagating flamefront, after which the power supply of the igniter is switched off andthe fuel valve to the igniter is closed.

The angle of the funnel 28 should not be too great, in order that theflame ball will be readily self-propelled therefrom. The included angleof the funnel may be from about 15 to about 40, with an angle of about30 having been found satisfactory.

What is claimed is:

1. In a gas turbine engine having a combustion chamher and a fuel supplyand means for delivering a fuel-air mixture to the combustion chamber,an igniting device wherein the improvement comprises:

a. a head member mounted on the combustion chamher and having a fuelconnection to receive fuel from the fuel supply and bearing a tubularwell extending into the combustion chamber, the well having an aperturedinner end wall;

b a tubular insulator positioned within the well and having an electrodedisposed therein, the insulator defining a spark path between theelectrode and the inner end of the well;

c. the tubular insulator having a smaller outer diameter than the innerdiameter of the well and defining an annular channel therewith, the headmember having passage means communicating between the fuel connectionand the annular channel, and the inner end of the insulator havingpassage means therein communicating between the annular channel and thespark path to deliver fuel thereto;

d. the inner end face of the insulator being seated against theapertured inner end wall of the well, the inner diameter of theinsulator at its inner end being funnel shaped with the larger diameterof the funnel adjacent to the end wall of the well, the aperture in theend wall of the well being approximately the same diameter as the largeend of the funnel; and

e. an electrical power supply connected to the electrode to initiate anarc across the spark path to vaporize and ignite the fuel in the sparkpath, the ignited fuel being propelled as a flame into the main fuel-airmixture.

2. The combination recited in claim 1, wherein the funnel portion of theinsulator has an included angle from about 15 to about 40, the electrodeextends inwardly into the insulator to a position approximately evenwith the smaller diameter of the funnel portion, and the spark path isalong the funnel wall between the electrode and the edge of the aperturethrough the inner end wall of the well.

3. The combination recited in claim 2, wherein the funnel portion of theinsulator has an included angle of approximately 30.

4. The combination recited in claim 3, wherein the electrode hasconnected thereto an electrical power supply capable of delivering about0.5 to 2 joules of stored electrical energy.

1. In a gas turbine engine having a combustion chamber and a fuel supplyand means for delivering a fuel-air mixture to the combustion chamber,an igniting device wherein the improvement comprises: a. a head membermounted on the combustion chamber and having a fuel connection toreceive fuel from the fuel supply and bearing a tubular well extendinginto the combustion chamber, the well having an apertured inner endwall; B. a tubular insulator positioned within the well and having anelectrode disposed therein, the insulator defining a spark path betweenthe electrode and the inner end of the well; c. the tubular insulatorhaving a smaller outer diameter than the inner diameter of the well anddefining an annular channel therewith, the head member having passagemeans communicating between the fuel connection and the annular channel,and the inner end of the insulator having passage means thereincommunicating between the annular channel and the spark path to deliverfuel thereto; d. the inner end face of the insulator being seatedagainst the apertured inner end wall of the well, the inner diameter ofthe insulator at its inner end being funnel shaped with the largerdiameter of the funnel adjacent to the end wall of the well, theaperture in the end wall of the well being approximately the samediameter as the large end of the funnel; and e. an electrical powersupply connected to the electrode to initiate an arc across the sparkpath to vaporize and ignite the fuel in the spark path, the ignited fuelbeing propelled as a flame into the main fuel-air mixture.
 2. Thecombination recited in claim 1, wherein the funnel portion of theinsulator has an included angle from about 15* to about 40*, theelectrode extends inwardly into the insulator to a positionapproximately even with the smaller diameter of the funnel portion, andthe spark path is along the funnel wall between the electrode and theedge of the aperture through the inner end wall of the well.
 3. Thecombination recited in claim 2, wherein the funnel portion of theinsulator has an included angle of approximately 30* .
 4. Thecombination recited in claim 3, wherein the electrode has connectedthereto an electrical power supply capable of delivering about 0.5 to 2joules of stored electrical energy.